1. Field of the Invention
This invention relates to a temperature compensating circuit in a camera provided with an electric shutter, and more particularly to a device for compensating for the temperature characteristic of a shutter mechanism such as a focal plane shutter or the like.
2. Description of the Prior Art
In the focal plane shutter of a camera, it is well known that the shutter time is faster or slower due to a variation in temperature. The reason is that the dimensions of the shutter forming member and the viscosity of the lubricating oil are varied by temperature. Such a nature is purely of a mechanism and is peculiar to each shutter.
In a camera having incorporated therein such a shutter mechanism, when it is desired to electrically control the shutter time, it is necessry to compensate for the temperature of the electric circuit which controls the shutter time as well as to compensate for the temperature characteristic of the shutter mechanism. The amount of variation of the shutter time is of the order of several hundred microseconds and therefore, it offers little problem when the shutter time is 1/500 sec. or less, although a variation in shutter time accompanies it. But if the shutter time is 1/1000, 1/2000, 1/4000 sec. etc., the variation in shutter time is non-negligible.
A device has heretofore been proposed in which the variation in dimensions of a bimetal element is utilized to adjust the timing of the movement of the shutter and to compensate for the temperature characteristic of the shutter mechanism. However, the variation in dimensions of the bimetal element takes place only in one direction with respect to temperature and, therefore, the temperature characteristic of the shutter mechanism which can be compensated for must be such that the variation in shutter time takes place in one direction with respect to temperature.
However, actual measurement of the temperature characteristics of the shutter mechanisms in commercially available cameras shows that there is a tendency for the shutter time to be slower on the opposite sides of a certain temperature where it peaks and such tendency cannot be completely compensated for by the prior art technique. In addition a space is required if it is intended to effect mechanical compensation. Further, the conventional control cam for the high-speed shutter time effects adjustment of the shutter time by step differences of the order of several tens of microns and this makes it difficult to effect the shutter time adjustment by the incorporation of a bimetal element. Moreover, such adjustment is combersome because it must be effected with the camera actually varied in temperature.